The invention relates in general to pumps and in particular to a new and useful control device for a fuel feed pump with an electromagnetically driven piston rod having one end with a control membrane and an opposite end with a control head adjustable in height.
Such pumps are used for fuel proportioning in motor independent heating systems using extra gasoline or diesel fuel. With them small quantities of fuel must be transported reliably. A metering pump is used for the dosage of the fuel. In the known applications for heating equipment with an output between 1000 and 20,000 kcal/h, fuel quantities of e.g. 0.2 to 3 liter/h must be conveyed in an even flow.
The simplest device for fuel transport results through the use of a float regulator with a membrane pump. The membrane pump conveys the fuel into a float regulator, in which the fuel level is maintained constant, relative to a fuel nozzle downstream of the fuel flow. This known device conveys the fuel quantity in a flow constant in time. It has the disadvantage that the fuel quantity must be adapted to the minimum conveyed combustion air quantity, so that the heater will not produce soot at underload.
Known also are metering pumps with pulse generators (see U.S. Pat. No. 3,699,354; German Pat. No. 12 73 992). These pumps are constructed as electromagnetic piston pumps. The electromagnet is designed as a solenoid, the pump piston moving in the interior thereof. These metering pumps work as volumetrically conveying pumps; at every current pulse the piston moves back and forth once, the suction stroke being brought about in the known devices by a return spring. These pumps operate independently of pressure without an after-connected nozzle, they convey fuel according to the number of strokes and displacement volume of the pump.
In these pumps the pulse generator forms an important part. As pulse generators are known e.g. according to German OS 17 63 735 (U.S. Pat. No. 3,380,387) control means where the pulse delivery occurs through a unit consisting of electric motor with a step-down transmission a permanent magnet and a transistor, there being arranged on the revolving part of a worm wheel driven by the motor a permanent magnet which cooperates with a magnetic switch and which in turn controls the base of a transistor through which the pump then receives its pulses. Such pumps are used exclusively as metering pumps. Further, arrangements have become known where the pulse generator consists of a perforated disc with a drive as well as of a photo diode and photo element, where the drive of the perforated disc is arranged on the drive shaft of the combustion air motor belonging to the heating system and where the perforated disc extends into the space between the photo diode and photo element, so that the ray path between photo diode and photo element is temporarily interrupted. These pumps can be used only as metering pumps and their operation is dependent on the parameters of the heating system. These known arrangements, however, are very costly and trouble prone and cannot be used as fuel pumps.